- Tree tech :
If I understand, Laser and Gauss can be developped at the same time. Bbut Laser focus to destruction with scater and Gauss focus to accuracy with sniper ?
Sort of, but it's a bit more complicated:
Advantages of laser:
Better damage type,
Auto-fire,
Faster shooting (especially snap shots),
(ultimately) Unlimited ammo,
Lower weight,
(for craft cannon) Better range.
Advantages of gauss:
Higher damage,
Faster aimed shots,
More accuracy,
(for craft cannon) Better rate of fire.
This is just a general list of course, there are some nuances.
- Stun tech :
Other thing, do you think to include the Dart Rifle in adv weapon ? We can lowered power of alien stun bomb and to develop research for each alien biology and make special dart for each species ?
Yeah, I'd like to add Stun Rifle weapon too, if there are no objections. I think it's really fun, but I guess it depends on how late the Stun Launcher appears.
A separate clip for each species wouldn't be that good IMO. That would simply be too many clip types, for little gain (if any). Most aliens have similar physiology anyway (and similar to ours too).
As for the Stun Launcher itself, I would prefer not to change vanilla items without a good reason. I like it the way it is, even if it makes Dart Rifle obsolete at some point.
I finaly try Tazer, I found It too much powerfull. 22-25 May more balanced value. And Stun grenade for 15-18 ? 
I don't think it's too powerful at all. Bear in mind that it has such a short range that you can as well use a Stun Rod, which is much more powerful and cannot miss, and also has no clips (while taser has only 2 charges). Taser's best feature is that it is small and handy, otherwise I prefer the Stun Rod. If the taser was any weaker, it would be useless; besides, it's still not as strong as I (as a player) would like.
As for the Stun Grenade, I have never actually used them yet, so... no comment.
- Basic weapons :
Now I like shootgun with AC ammunition 
But may rebalanced it with lower accuracy.
Perhaps. It's way less accurate than the rifle, but stronger. More snap shots, but ultimately far less bullets per turn. Good for UFO storming, but so-so in the open field...
Oh damn, I just don't know.
For Sniper Rifle acuracy is too high too, 120%-130% is easy to reach, even if soldier can fire only once time.
The accuracyAimed value for the normal Rifle is 110. Sniper Rifle has to be better than that. Perhaps 160 is a bit much, yeah... But it's not much more than the Plasma Sniper Rifle. Well, I guess we could reduce all snipers - these two and the Gauss Sniper Rifle - by 10, but on the other hand they aren't very easy to use, so they need some advantage. If you think they're still too good, I'll reduce their accuracy a little, no problem. (Just remember that the Heavy Plasma Gun has accuracyAimed at 110, and it's not a sniper rifle at all.)
Flamme thrower : ouch ! need to rebalenced too. It useful in spaces will have been confined, but there is enormous collateral damage for the soldier who uses it. Finally I am not very convinced of the tactical value of this weapon.
This weapon is more for fun than anything else, but I find it moderately useful. Still, I agree it can be better balanced, I'm just not sure how. Perhaps a simple increase in max range would be enough?
EDIT: I've attached an Excel file with stats for all weapons I'm using personally, from various mods. Most of them, if not all, I would like to see in our project, so it may be useful for everyone.
